A MODEL FOR THE SYNTHESIS AND OPTIMIZATION OF HYBRID RO-MSF DESALINATIONS PLANTS

MARIAN G. MARCOVECCHIO; PÍO A. AGUIRRE; NICOLÁS J. SCENNA

Rio de Janeiro, Brasil

Congreso; 2nd Mercosur Congress on Chemical Engineering and 4th Mercosur Congress on Process Systems Engineering; 2005

UFRJ

Abstract. A model for the synthesis and optimization of hybrid RO-MSF desalination plants is presented.  flash process, fresh water is obtained by applying thermal energy to seawater feed in multiple stages creating a distillate stream for fresh water uses, and a concentrate (brine) stream that is returned to the sea. In RO process, the seawater feed is pumped at high pressure to special membranes, forcing fresh water to flow through the membranes. The concentrate (brine) remains on the upstream side of the membranes, which is passed through an energy recovery device before being discharged back to the sea. The MSF process has a high consumption of energy mean while RO is a lower energy demanding process. However, the membrane replacement and the high-pressure pumps increase the RO plant cost. Then, the hybridization of both methods must be considered. Although the model for the MSF process was derived from simplified hypothesis, it considers all the most important aspects of the process. The model takes into account the evaporator geometric design, height, length and width of stages, number of tubes in the pre-heater, Boiling Point Elevation, among others. The RO network was designed by using hollow fibre reverse osmosis modules. The Kimura-Sourirajan model was used for describing transport phenomena of solute and water transport through the membrane. The concentration polarization phenomenon has been taken into account. It was mathematically described using the film theory. The model presented integrates the different possible configurations for a hybrid plant combining MSF and RO processes. The objective is to determine the optimal process design structure and operating conditions for a given water production. The objective function to be minimized is the cost, which includes: capital investment and operation and maintenance costs. A model for the synthesis and optimization of hybrid RO-MSF desalination plants is presented.  flash process, fresh water is obtained by applying thermal energy to seawater feed in multiple stages creating a distillate stream for fresh water uses, and a concentrate (brine) stream that is returned to the sea. In RO process, the seawater feed is pumped at high pressure to special membranes, forcing fresh water to flow through the membranes. The concentrate (brine) remains on the upstream side of the membranes, which is passed through an energy recovery device before being discharged back to the sea. The MSF process has a high consumption of energy mean while RO is a lower energy demanding process. However, the membrane replacement and the high-pressure pumps increase the RO plant cost. Then, the hybridization of both methods must be considered. Although the model for the MSF process was derived from simplified hypothesis, it considers all the most important aspects of the process. The model takes into account the evaporator geometric design, height, length and width of stages, number of tubes in the pre-heater, Boiling Point Elevation, among others. The RO network was designed by using hollow fibre reverse osmosis modules. The Kimura-Sourirajan model was used for describing transport phenomena of solute and water transport through the membrane. The concentration polarization phenomenon has been taken into account. It was mathematically described using the film theory. The model presented integrates the different possible configurations for a hybrid plant combining MSF and RO processes. The objective is to determine the optimal process design structure and operating conditions for a given water production. The objective function to be minimized is the cost, which includes: capital investment and operation and maintenance costs.